The present invention relates to a plastic film for medical liquid containers and more particularly to a plastic film suitable for use as a material from which to form medical liquid containers such as bags for transfusions, drug solutions, and blood.
There have been proposed a variety of materials from which to form medical liquid containers to hold transfusions, drug solutions, and the like. For example, there is disclosed in Japanese Patent Laid-open No. Hei 8-252298, a plastic film for medical liquid containers which is composed of an oriented plastic surface layer, an adhesive resin layer, an oriented polyethylene or polypropylene layer, and a sealant layer directly fusion-bonded to the oriented polyethylene or polypropylene layer. The layers are directly laminated to each other without any anchoring agent and adhesives interposed between them. There is also disclosed in Japanese Patent Laid-open No. Hei 9-75444, a base material for medical use in which the layers contain a block copolymer composed of a random copolymer composed mainly of propylene and a polymer composed mainly of xcex1-olefin other than propylene. There is disclosed in Japanese Patent Laid-open No. Hei 9-85913 a plastic film for liquid containers which is composed of a transparent base film and a polypropylene-based film laminated on at least one side of the transparent base film, the latter being incorporated with syndiotactic polypropylene, isotactic polypropylene copolymerized with ethylene, and/or olefin-based elastomer.
Moreover, there is disclosed in Japanese Patent Laid-open No. Hei 9-308682, a plastic film for medical liquid containers which has a sealant layer composed of at least two layers of mixed film directly laminated to each other without any adhesives interposed between them. The films are formed from a mixture of high-density polyethylene having a density no lower than 941 kg/m3 and linear low-density polyethylene having a density of 900-940 kg/m3 in varied mixing ratios. There is also disclosed in Japanese Patent Laid-open No. Hei 9-308683 a plastic film for medical liquid containers which has a sealant layer composed of at least two layers of mixed film directly laminated to each other without any adhesives interposed between them. The films are formed from a mixture of high-density polyethylene having a density no lower than 941 kg/m3 and linear low-density polyethylene having a density of 900-940 kg/m3 in varied mixing ratios. The sealant layer is laminated to the upper and lower sides of a transparent film, with adhesives interposed between them, such that the transparent film is bonded to the mixed film layer in which the mixing ratio of the high-density polyethylene is lower.
In addition, there is disclosed in Japanese Patent Laid-open No. Hei 10-323381 a medical container formed from a multi-layered film constructed of an intermediate layer and an inner layer directly adjacent to the inside thereof. The intermediate layer is formed from a mixture of ethylene-vinyl alcohol copolymer and styrene resin. The inner layer is formed from any of a resin composed mainly of modified polyolefin, a first mixed resin composed mainly of modified polyolefin and styrene resin, and a second mixed resin composed mainly of polypropylene resin and styrene resin. There is also disclosed in Japanese Patent Laid-open No. Hei 11-290422 a transfusion container formed from a multilayered sheet composed of an outer layer and an inner layer. The outer layer contains a polymer composition of polypropylene block copolymer and hydrogenated butadiene-styrene polymer. The inner layer contains any of (a) polypropylene block copolymer, (b) polypropylene random copolymer, and (c) polymer composition of the polypropylene block copolymer or polypropylene random copolymer and hydrogenated butadiene-styrene polymer. The melting point of the outer layer is higher than the melting point of the inner layer by 10xc2x0 C. or more.
Moreover, there is disclosed in Japanese Patent Laid-open No. 2000-14747 a medical container having a triple-layered wall which is constituted such that the inner and outer layers are composed mainly of high-density polyethylene (HOPE) and the intermediate layer is composed mainly of linear low-density polyethylene (LLDPE), with the total thickness of the inner and outer layers being no larger than 80 xcexcm and no smaller than 10 xcexcm. The HOPE has a density no lower than 945 kg/m3 and a peak temperature no lower than 125xc2x0 C. (measured by a differential scanning calorimeter). The LLDPE is obtained by means of metallocene catalyst having a density of no lower than 925 kg/m3 and no higher than 935 kg/m3. There is disclosed in Japanese Patent Laid-open No. 2000-33674, a medical container of multi-layered laminate film at least composed of a first layer (as the inner most layer), second layer (as a bonding layer), and third layer. The first layer is formed from a mixture of polypropylene and/or polyethylene resin and styrene resin. The second layer is formed from modified polyolefin, and a third layer is formed from ethylene-vinyl alcohol copolymer on the outer side of the first layer.
None of the disclosed plastic films for medical liquid containers, however, do not meet all the requirements for heat resistance, transparency, haze, heat-sealability, drop strength, impact strength, and flexibility. The laminate film having a bonding layer such as adhesives and adhesive resin tends to permit organic matters to dissolve in the content liquid. The plastic film of propylene block copolymer is hazy (or poor in transparency) although it is improved in drop strength and impact strength. High haze prevents the inspection of the content liquid.
The disadvantage of the film incorporated with a thermoplastic elastomer for improvement in film flexibility is that the thermoplastic elastomer presented on the surface layer causes sticking and hampers handling. Moreover, such thermoplastic elastomer whitens immediately after sterilization with high-pressure steam, thereby preventing the inspection of the content liquid. Moreover, the thermoplastic elastomer (excluding propylene-based elastomer) contained in the innermost layer (in contact with liquid) causes not only whitening and sticking but also tends to permit organic matters to dissolve in the content liquid. This is undesirable for medical containers. The container with an intermediate layer containing elastomer, such as mixed layer with ethylene-vinyl alcohol copolymer, has improved gas barrier properties for existence of ethylene-vinyl alcohol copolymer but is subject to whitening upon sterilization with high-pressure steam. Whitening prevents the inspection of content liquid.
Moreover, the container with an intermediate layer formed from elastomer alone is subject to whitening as well as dissolution in the content liquid and it is high in production cost. The plastic film for medical liquid containers should preferably be capable of high-frequency fusion cutting and sealing from the standpoint of efficient operation if it is to be fabricated into containers by using the existing bag-making machines for polyvinyl chloride materials.
The present invention was completed in view of the foregoing. It is an object of the present invention to provide a plastic film for medical liquid containers which is characterized by such properties as weak tendency toward whitening by sterilization with high-pressure steam, ability to permit the inspection of content liquid immediately after sterilization with high-pressure steam, freedom from sticking (which leads to easy handling of the resulting containers), good flexibility, high drop strength and impact strength, insolubility in the content liquid upon sterilization with high-pressure steam at 121xc2x0 C., nontoxicity, ability to be fabricated into safe medical liquid containers, and capability of heat-sealing as well as high-frequency fusion-sealing (which permits fabrication by the existing bag-making machine for polyvinyl chloride materials). These properties are required of the material from which the medical liquid containers are fabricated.
To achieve the above-mentioned object, the present invention is directed to a plastic film for medical liquid containers which includes at least three layers, each layer not containing non-elastomeric block copolymer of benzene-ring-free olefin and propylene, such that the first layer, which is composed mainly of propylene homopolymer, the second layer, which contains polypropylene resin, polyethylene resin, and thermoplastic elastomer, and the third layer, which functions as a sealing layer and is composed mainly of copolymer of propylene and other monomers, are laminated without the aid of bonding layer, with the second layer acting as an intermediate layer.
According to a preferable embodiment, the first layer is composed mainly of a propylene homopolymer which is a mixture of two or more kinds of propylene homopolymer in a ratio of from 1:9 to 9:1 (by weight), the first one having a melt flow rate of 0.1-5 g/10 min at 230xc2x0 C. and a density of 880-913 kg/m3, and the second one having a melt flow rate of 5-50 g/10 min at 230xc2x0 C. and a density of 880-913 kg/m3, such that the resulting mixture has a melt flow rate no higher than 5 g/10 min at 230xc2x0 C.
According to another preferred embodiment, the second layer is composed of 50-85 parts by weight of the polypropylene resin, 5-30 parts by weight of the polyethylene resin, and 10-40 parts by weight of the thermoplastic elastomer. In addition, the polypropylene resin contained in the second layer is a random copolymer of propylene and ethylene, with the ethylene content being 5-30% by weight; the polyethylene resin contained in the second layer is a linear low-density polyethylene having a melt flow rate of 0.1-10 g/10 mm at 190xc2x0 C. and a density of 850-980 kg/m3; and the thermoplastic elastomer contained in the second layer is a styrene-based elastomer.
According to a further preferred embodiment, the second layer contains a resin capable of high-frequency dielectric heating, so that it permits high-frequency fusion cutting and sealing. The resin capable of high-frequency dielectric heating should preferably be a polyamide resin.
According to another preferred embodiment, the third layer contains a copolymer which is a random copolymer of propylene and ethylene, with the ethylene content being 5-30% by weight. The copolymer contained in the third layer should preferably be a random copolymer of propylene which has a melt flow rate of 1-8 g/10 min at 230xc2x0 C. and a density of 850-980 kg/m3. The copolymer of propylene and other monomers which is contained in the third layer should preferably be a non-elastomeric copolymer of propylene and other monomers, a propylene-based elastomer, or a mixture of the non-elastomeric copolymer and the propylene-based elastomer.
According to another preferred embodiment, the plastic film for medical liquid containers has a total light transmission no lower than 85% (according to JIS K7105) and a haze value no higher than 25% according to JIS K7105) measured immediately after sterilization with high-pressure steam at 121xc2x0 C. for 30 minutes. According to a further preferred embodiment, the plastic film for medical liquid containers has a tensile elastic modulus no higher than 300 MPa according to JIS K7127) measured immediately after sterilization with high-pressure steam at 121xc2x0 for 30 minutes.
According to another preferred embodiment, the first layer has a thickness of 5-20 xcexcm, the second layer has a thickness of 100-300 xcexcm, and the third layer has a thickness of 30-120 xcexcm.
According to the present invention, the plastic film for medical liquid containers does not contain in any of its layers a non-elastomeric block copolymer of benzene-ring-free olefin and propylene. Therefore, it has high transparency and low haze and is free from whitening and clouding. It undergoes very little whitening after sterilization with high-pressure steam at 121xc2x0 C. In addition, it has good heat resistance because its first layer is composed mainly of propylene homopolymer. This first layer contributes to the film cutting ability (without stringing) at the time of high-frequency fusion cutting and sealing.
In addition, the second layer as an intermediate layer contains most of the thermoplastic elastomer which causes a problem of dissolution. This imparts non-sticky feel and gets around whitening and dissolution due to sterilization with high-pressure steam at 121xc2x0 C. The fact that the second layer contains, in addition to a thermoplastic elastomer, polypropylene resin (PP resin for short hereinafter) and polyethylene resin (PE resin for short hereinafter) effectively prevents whitening and contributes to cost reduction.
Moreover, the third layer, which functions as a sealing layer, is composed mainly of a copolymer of propylene and other monomers. This provides sufficient heat-sealing strength. The plastic film is fabricated into medical liquid containers in such a way that the third layer becomes the innermost layer. Thus, the resulting medical liquid containers have sufficient drop strength and impact strength.
According to the present invention, these layers are laminated on top of the other without the help of a bonding layer. Therefore, the medical liquid containers formed from the plastic film of the present invention are exempt from problems of dissolution in the content liquid by adhesives or adhesive resin after sterilization with high-pressure steam. In addition, the thermoplastic elastomer which causes a problem of dissolution is confined mainly in the second layer which functions as an intermediate layer and the resin capable of high-frequency dielectric heating is also confined in the second layer. This avoids problems of dissolution from the thermoplastic elastomer and the resin capable of high-frequency dielectric heating.
According to the present invention, the propylene homopolymer constituting the first layer is a mixture of two or more kinds of propylene homopolymer. A first propylene homopolymer (A) has a melt flow rate (MFR for short hereinafter) of 0.1-5 g/10 min at 230xc2x0 C. and a density of 880-913 kg/m3. A second propylene homopolymer (B) has an MFR of 5-50 g/10 min at 230xc2x0 C. and a density of 880-913 kg/m3. They are mixed in a ratio (A:B) of from 1:9 to 9:1 such that the resulting mixture has an MFR no higher than 5 g/10 min at 230xc2x0 C. Such a mixture is superior in film-forming properties and gives rise to a strong film. Incidentally, MFR is measured according to JIS K7210.
In addition, the second layer may contain a mixture of 50-85 parts by weight of the PP resin, 5-30 parts by weight of the PE resin, and 10-40 parts by weight of the thermoplastic elastomer. The PP resin contained in the second layer may be a random copolymer of propylene and ethylene, with the ethylene content being 5-30% by weight. In this case, the medical liquid container formed from the plastic film is superior in impact resistance, drop strength, transparency, and haze. Restricting the ratio of thermoplastic elastomer in the second layer as mentioned above effectively contributes to cost reduction.
In addition, the PE resin contained in the second layer may be a linear low-density polyethylene (LLDPE for short hereinafter) having an MFR of 0.1-10 g/10 min at 190xc2x0 C. and a density of 850-980 kg/m3, or the thermoplastic elastomer contained in the second layer may be a styrene-based elastomer. This contributes to prevention of whitening and improvement in transparency and haze.
Moreover, the second layer may contain, in addition to the mixture resin, a resin capable of high-frequency dielectric heating so that the resulting plastic film is suitable for high-frequency fusion cutting and sealing. In this case, the plastic film can be fabricated into medical liquid containers by means of the existing bag making machine for polyvinyl chloride materials. Such a bag making machine can perform film cutting and peripheral sealing simultaneously. The resin capable of high-frequency dielectric heating may be a polyamide resin. In this case, it is possible to achieve better sealability by high-frequency fusion cutting and sealing. The fact that the resin capable of high-frequency dielectric heating is confined in the second layer (as an intermediate layer) and isolated by the third layer prevents the resin from dissolving in the content liquid.
Moreover, the copolymer contained in the third layer may be a random copolymer of propylene and ethylene, with the ethylene content being 5-30% by weight, or a random copolymer having an MFR of 1-8 g/10 min at 230xc2x0 C. and a density of 850-980 kg/m3. In this case, the resulting plastic film is much better in seal strength, impact strength, and drop strength.
In addition, the third layer may contain a copolymer of propylene with other monomers, the copolymer being selected from (a) non-elastomeric copolymer of propylene with other monomers, (b) propylene-based elastomer, and (c) a mixture of (a) and (b) mentioned above. In this case, the resulting plastic film is further improved in flexibility, impact strength, and drop strength. Of thermoplastic elastomers, the propylene-based elastomer is preferable because it causes no problems with sticking, whitening, and dissolution. The third layer containing such an elastomer is safe and easy to handle when it is in contact with the medical liquid. Incidentally, according to the present invention, the third layer is composed mainly of a copolymer of propylene with other monomers; however, it may be incorporated with any olefin-based elastomer (other than the propylene-based elastomer) in an amount not harmful to the effect of the present invention as a matter of course.
According to another preferred embodiment, the plastic film for medical liquid containers has a total light transmission no lower than 85% (according to JIS K7105) and a haze value no higher than 25% (according to JIS K7105) measured immediately after sterilization with high-pressure steam at 121xc2x0 C. for 30 minutes. According to a further preferred embodiment, the plastic film for medical liquid containers has a tensile elastic modulus no higher than 300 MPa (according to JIS K7127) measured immediately after sterilization with high-pressure steam at 121xc2x0 C. for 30 minutes. In this case, the plastic film gives rise to medical liquid containers which hardly subject to whitening due to ordinary sterilization with high-pressure steam and which readily permits the inspection of content liquid immediately after sterilization with high-pressure steam. This contributes to total cost reduction in the production line.
Furthermore, the first layer may have a thickness of 5-20 xcexcm, the second layer may have a thickness of 100-300 xcexcm, and the third layer may have a thickness of 30-120 xcexcm. In this case, the plastic film is superior in flexibility and gives rise to the medical liquid containers which have good drop strength and are protected from dissolution from the thermoplastic elastomer in the second layer and the resin capable of high-frequency dielectric heating.
As mentioned above, the plastic film for medical liquid containers as covered in the present invention is superior in transparency, flexibility, non-sticky touch, heat resistance, strength, and sealability. It gives rise to medical liquid containers superior in flexibility, impact strength, and drop strength, and free from dissolution in the content liquid upon sterilization with high-pressure steam. In addition, it is non-toxic and hardly subject to whitening immediately after sterilization with high-pressure steam. This facilitates the rapid inspection of the content liquid immediately after sterilization with high-pressure steam. The medical liquid containers can be formed by high-frequency fusion cutting and sealing. Thus, the plastic film of the present invention is useful as a material from which to make medical liquid containers.